Preservation of CO2 Hydrates with Cyclopentane and Ethylcyclohexane near the Melting Point of Ice under Atmospheric Pressure

In this study, we investigated the preservation of CO₂ hydrates in organic liquids near the melting point of ice at atmospheric pressure under isothermal temperature conditions to enable CO₂ storage and transportation using gas hydrates under milder temperature and pressure conditions. Cyclopentane (CP), ethylcyclohexane (ECH), and 2-ethyl-1-hexanol (2-EH) were used as organic liquids and their effects on the dissociation behaviors of the CO₂ hydrate were evaluated. After 24 h, the preservation ratios of CO₂ hydrate powders with CP or ECH were ∼70% at 265 K and ∼60% at 269 K. In contrast, the preservation ratios without organic liquids were ∼30% at 265 K and ∼10% at 269 K. The analysis revealed that CP promoted the formation of CP hydrate shells on the CO₂ hydrate surface during dissociation, whereas ECH facilitated ice shell formation. However, the CO₂ hydrate with 2-EH dissociated rapidly within approximately 1 h at 265 and 269 K because 2-EH inhibited ice shell formation. These results indicate that hydrophobic CP and ECH enhance the CO₂ hydrate stability by enabling the formation of shell structures by CP hydrate or ice that encapsulates the hydrates and prevents CO₂ gas release.